An electric motor has a rotor and a stator. The stator includes a stator core, in which motor coils are respectively wound on tooth sections and an insulator. To increase performance of the motor, a magnet wire is wound in open slots, which are formed between tooth sections of the stator core, as much as possible, so as to increase space factor of the coils.
Conventionally, a nozzle of a coil winding machine is inserted into an open slot, which is formed between tooth sections of a stator core, in a laminating direction of the stator core, so as to wind a magnet wire to form a coil.
For example, a case of a winding magnet wire on a stator core of three-phase/12-slots DC brushless motor will be explained. Tooth sections are named, in the counterclockwise direction, a first tooth section, a second tooth section . . . . In case of winding a U-phase coil, the magnet wire is wound on the first tooth section, then the magnet wire is extended to an outer circumference of an insulator, crossover-wired and wound on the fourth tooth section, further the magnet wire is extended to the outer circumference of the insulator, crossover-wired and wound on the seventh tooth section and the tenth tooth section in the same manner.
Next, the magnet wire is extended to the outer circumference of the insulator and crossover-wired, then a V-phase coil is wound on the adjacent eleventh tooth section. Further, the magnet wire is extended to the outer circumference of the insulator, crossover-wired and wound on the second tooth section. Then, the magnet wire is extended to the outer circumference of the insulator, crossover-wired and wound on the fifth tooth section and the eighth tooth section in the same manner.
Next, the magnet wire is extended to the outer circumference of the insulator and crossover-wired, and a W-phase coil is wound on the adjacent ninth tooth section. Then, the magnet wire is extended to the outer circumference of the insulator, crossover-wired and wound on the twelfth tooth section, the third tooth section and the sixth tooth section, in order, in the same manner.
As shown in FIG. 7, an insulator 52, which is attached to a stator core 51, has guide projections 53, which are projected from the stator core and act as guides for extending a magnet wire 54. A coil is wound on each of tooth sections, and the magnet wire 54 extended to outer circumference of the guide projection 53 is crossover-wired to a next tooth section. For example, an intersecting section 55, in which a crossover wire of a U-phase 54a and a crossover wire of a V-phase 54b intersect with each other, is formed. To reduce an axial length of an electric motor, heights of the crossover wires of the tooth sections are lowered, so that the crossover wires are forced to intersect with each other.
Therefore, for example, if the electric motor having the intersecting section 55, in which the crossover wires 54a and 54b intersect with each other, is continuously used in a state where vibration is applied to the electric motor, problems, e.g., peeling of an insulation film of the magnet wire 54, will occur.
To remove a burden of covering adjacent crossover wires with protection tubes, a stator of an electric motor, in which axial notches with different depths are formed in an insulator (bobbin) and crossover wires are separated by guide projections, have been invented (see Japanese Laid-open Patent Publication No. 2001-103698).
In the insulator (bobbin) disclosed in Japanese Laid-open Patent Publication No. 2001-103698, when the magnet wire wound on one tooth section is extended and crossover-wired to another tooth section, extending positions, from which the magnet wire is outwardly extended, are defined by the notches. Further, when the magnet wire is crossover-wired along outer circumference of the insulator, the crossover wires are separated by the guide projections, so that no crossover wires contact each other. Therefore, electrical contact of the crossover wires can be prevented, and an insulating process can be omitted.
However, an axial length of the insulator must be increased by a thickness of the guide projections, and wiring areas of the crossover wires must be extended in the axial direction. Therefore, it is difficult to downsize the motor in the axial direction.
Further, a position of a terminal, to which a starting end of the coil is connected, and a position of another terminal, to which a terminating end of the coil is connected, are predetermined. Therefore, when the magnet wire is wound by a coil winding machine, the positions of the terminals must be confirmed before setting the stator in the coil winding machine, so set errors will easily occur.